Fuel Gas From Cowdung 1983 PDF
Preview Fuel Gas From Cowdung 1983
A project of Volunteers in Asia Fuel Gas from Cowdung by B.R. Saubolle and A. Bachmann Published by: Szhayogi Press Tripureshwar Kathmandu NEPAL Available from: UNICEF P.O. Box 1187 Kathmandu NEPAL Reproduced by permission. Reproduction of this microfiche document in any form is subject to the same restrictions as those of the original document. B.R. SAUBOLLE . ~A~~~A~N FUEL GAS FROM CO THIRD EOITION E3.R.SAUBOLLE AN0 A.BACHMANN SAHAYOGI PRESS KATHMANOU Published by: Sahayogi Press Tripureshwar Kathmandu First Edition : April 1976 Second Edition : April 1980 Third Edition : September 1983. Copyright is reserved by the authors, but permission is hereby granted for the reproduction of any part w text or drawing, for non-profit publication; however, tile whole booklet, or any major portion should not be reproduced without permission. Anyone making use of material presented herein should acknowledge the source and submit to the authors a copy of the excerpt. Printed in Nepal at Sahayogi Press THIS BOOKLET IS DEDICATED TO THE MILLIONS OF VILLAGERS IN THE HIMALAYAN KINGDOM OF NEPAL WHOSE NEED FOR FUEL HAS BEEN THE AUTHORS’ SOLE REASON FOR WRITING IT, 1 GRANT YOU COWDUNG. YOU ARE TO BAKE Y3UR BREAD ON THAT, EZEKIEL 4.15 Rev. Saubolle is the pioneer of biogas in Nepal. His oil drum plant, built in 1960 at St. Xavier's School in Godavari, twenty kilometers south-east of Kathmandu, was used for boiling tea, which "Father" offered to his guests. The biogas plant offered brilliant demonstration of fuel from waste long 'before it became "fashion- able". Many of us here in Nepal were inspired by his pioneering work. Late Rev. B.R. Saubolle, S.J. 1904 - 1982 Rev. B. Saubolle came to Nepal in the early fifties, and loved this country. A versatile man and a great thinker of things small and beautiful.His interests ranged from bee-keeping, roses, solar heating, to orchid cultivation. To many villagers of Godava,r..i ) “Pn+her” w -i--e- WBS a man they were proud to call a friend and one of their own kind. BIOGAS NEWSLETTER CONTENTS Preface Introduction -. Gas Production Slurry Pit Volume output and Temperature - Output and Pressure Consumption - Nature of Gas Points to be considered before constructing a Plant Data Sheet Gas Drums Constructing a Plant - The Pit - Input - Paddle-Wheel Mixer - Gas Outlet L Moisture Release = Gas Drums - Flame Trap - Gas Pipe Line Dimensions Using the Gas - Burners -Lamps - Running Engines 9 10 11 11 12 13 15 16 18 19 21 24 25 25 27 29 30 34 37 38 40 47 50 Double Chamber Construction 54 Gas in Bags -.__ .__-- 62 Stirrer or No Stirrer? _ 64 Gas from Night Soil 67 A Biogas Demonstration Plant 70 Chinese Biogas Technology 73 A Nepali Version of the Chinese Design --- 94 A Comparison: Chinese vs. Indian 99 Possible Troubles 101 Temperature Table - 102 PREFACE It was slightly more than a quarter century ago that biogas plants first appeared as a practical source of renewable alternative energy. The idea took time to catch on and to be accepted, but these plants are now in world-wide use. In a recent five- year plan India set itself the task of installing 25,000 cowdung gas plants a year. China claims at present the present moment to have some 7,000,000 biogas plants scattered all over the country, ranging from small family plants to huge government installa- tions for running buses, trucks and diesel-electric generators, besides steadily providing a collosal amount of rich fertilizer and humus for field and garden. The welcome given to FUEL GAS FROM COWDUNG by readers around the world has been very heartening. Since it first appeared it has several times been reprinted at the special request of UNICEF. We have the pleasure in offering the public the present third edition, which we hope will be still more useful to readers in developing countries. In preparing this edition we have borrowed rather freely from articles which have appeared in the BIOGAS NEWSLETTER of Nepal. For permission to do so we are grateful to the Editors. We wish also to thank the Development and Consulting Services (D.C.S.) of Butwal, Nepal, for kindly allowing us to include designs of several appliances produced and perfected by them. B.R. Saubolle, S.J. Andreas Bachmann INTRODUCTION People living in remote areas of South-East Asia, or other tropical or sub-tropical countries, where electricty is not available and fuel is hard to get, have a very cheap, abundant and efficient fuel in the gas produced from ordinary cowdung. This gas (marsh gas or methane) is generated with the greatest ease simply by letting a slurry of cowdung and water ferment in a ;Yell-like pit without exposure to air. The gas rises LO the surface and collects in a drum, whence it is piped to the kitchen stove. A farmer with a couple of bulls or buffaloes for ploughing and one or two cos for milk gets enough dung every day to produce sufficient gas for all the cooking needs of a village family of six. The cooking is clean and hygienic, the pots do not get black, there is no smoke or smell, and the gas is non-toxic. And after extracting the gas to cook his food, and to light his house at night, the farmer still has all the dung left, well fermented and rotted, to fertilize his fields. 11 GAS PRODUCTION TIME Fresh cowdung, or other animal dung (from horses, mules, donkeys, buffaloes, yaks, Pigs, pou3try) diluted with water and fermented by bacterium methano- genes, without exposure to air, delivers 90% of its potential gas within a period of four weeks, more than half of it within the first eight or ten days. Six weeks of fermentaticn produces about 98%. Hence the fermenting pit, in which daily additions \,f slurry enter at the bottom and gradually raise to overflow at the top, should be large enough to hold each day's addition for a minimum of four weeks or a maximum of six, i.e. from 30 to 40 days. In other words, the volume of the pit should be at least 30 times, or better 40 times, the volume of siurrjr added daily. SLURRY The optimum dilution of fresh dung with water for making the slurry is one that contains from 7% to 9% solid matter, the peak being 896, Hydrometer readings show a specific gravity of approximately 1.030 for 7% and 1.190 for 9%. 8% falls around 1.100. The right percentage is obtained automatically by mixing a given volume of dung with from one to one-and- a-half times the volume of water. The fact that thousands upon thousands of gas plants have been working satisfactorily for decades without the use of an hydrometer proves that this instrument, useful though it may be, is not strictly necessary. A good slurry is one in which the dung is broken up thoroughly and makes a smooth, even mixture having the consistency of thin cream. If the slurry is too thin, the solid matter separates and falls to the bottom instead of remaining in suspension; if it is too thick, the gas cannot rise freely to the surface. In either case the output of gas is less. It has been found that the optimum pH for digesting slurry is around 8. When starting a plant, the early fermentation is acid and much carbon dioxide is given off; but the acidity gradually diminishes, and once the contents of the pit become alcaline, methane generation predominates. If the pit is over- loaded, or the slurry too thick, acidity increases, much carbon dioxide is formed, and the gas won't burn, May users prefer a proportion of 1:l l/4 (4 parts dung to 5 parts water) and enjoy trouble- free operation. The acidity of the effluent is measured with pH paper (narrow-range: 6-9). It should read from 8 - 8.5, which is slightly more alkaline than the effluent of a municipal sewage plant. VOLUME OF PIT As was said above, the fermenting pit should have a volume from 30 to 40 times the slurry added daily. Thus: PROPORTION DUNG WATER SLURRY VOLUME OF PIT (x 30 or 40) = 1:l 2.5 cft 2.5 cft 5 cft 150 or 200 cft 1:l l/4 2.5 cft 3.1 cft 5.6 cft 168 or 224 cft 1:l l/2 2.5 cft 3.75 cft 6.25 cft 187 or 250 cft OR 1:l 75 ltr 75 ltr 150 ltr = 4500 or 6000 ltr 1:l l/4 75 1tr 94 1tr 170 1tr = 5100 or 6800 ltr 1:l l/2 75 1tr 112 ltr 187 ltr = 5610 or 7480 ltr It is recommended to use 1:l or 1: 1 l/4 and lnake the pit 40 times the daily slurry. Experience has shown that Indian villagers consume on an average 15 cft (425 ltr) of gas per person per day. So for a family of six about 100 cft (say 3000 litres) of gas would suffice. This output would require a pit of at least double that volume, 200 cft or 6000 litres, say 5 ft (1.5 m) diameter by 11 ft (3.40 m) dep, tkaing 2 l/2 cft or 75 litres of fresh dung every day. Allow 12 litres fresh dung per person per day. 13 BACTERIA For starting a new Plant, the necessary bacteria may be obtained from one of the following sources: a) Spent slurry from another gas plant; b) Either sludge or overflow water from a septic tank; c) Horse dung or pig dung, both rich in bacteria; d) Oooze from the bottom of any dirty pool. Without added bacteria fermentation may take about a month to get started. OUTPUT AND TEMPERATURE At a temperature of 85 OF ( 30 OC), 1 cft of dung delivers 40 cft of gas in four weeks; so that if, for example, 5 cft are added daily, the daily output of gas will be about 200 cft. This is not a mathe- matical constant: it is an average depending on the health and feed of COWS. At higher temperatures the output is greater, being 50 cft or more at 90 degrees F, while at 55O it drops to about 20 cft. MEAN TEMPERATURE OUTPUT OF GAS REMARKS DURING MONTH (cft/lb.dung) (ltr/kg dung) 85oF 1 1 29W or over 1.5 92.7 Excellent 75°F 24% 1.0 61.8 Good working average 65oF 1 18% 0.8 49.5 Serviceable 55OF , 12oC 0.5 30.8 Hardly worthwhile In places where for the greater part of the year the mean temperature is 18 OC (65 OF) or more, a gas plant is really worthwhile. In winter the gas will diminish unless something is done to warm the digesting slurry. Several methods are commonly recom- mended: 1 - DEPTH - Depth is a help. In the tropics and lower temperature latitudes, even in the Himalayas at 5000 ft.; the temperature at 4 m below ground, hardly drops lower than 15 OC. especially if the slurry is added hot, and some gas can be produced. 14 2 - INSULATION - Fermenting slurry generates practically no heat (only about 3 *C>. Pit temperature is only slightly higher than the outside air. Yet if the little heat generated is prevented from dissi- pating by conduction, something is gained. The insula- ting material must be kept quite dry. If damp, it CEUI chill instead of keeping warm. In the tropics it should also be something that white ants will not eat. 3 - HOT SLURRY - This helps a little. The daily input is in the order of only 2.5% of pit volume, so that it cannot make very much difference, but it is certainly more helpful if the slurry is hot (35 OC) rather than chillingly cold. 4 - HEATING COIL - When building a pit, a coiled pipe of 2" diameter can be installed inside. It is recommended to allow 1000 cm2 of coil area per 3 m3 of pit volume (1 sq.ft./lOO cft.). The coil should be heated with water not more than 60 OC (140 OF) or the slurry will cake on the coil surface, A thermostat set at 35 OC (95 OF) should be installed in the slurry. The gas used in heating the coil is repaid three times over by the increase of output. Heating could also be done by solar collectors. 5 - COMPOST TROUGH - Some users build a trench around the upper half of the pit and make compost in it. The heat generated by the composting organic matter keeps the pit warm. 6 - PLASTIC TENT - If the pit and a couple of metres of ground all around it are enclosed in a glass or clear plastic structure, the hot-house effect keeps the slurry warm. A few years ago it was claimed that this system kept gas plants function- ing in Korea in the midst of snow and ice; but our own investigation on the spot has led us to doubt its efficacy. However, we do believe that in milder winters (above freezing), the plastic tent may really be useful. We have not experimented with this ourselves. 15 7 - SURFACE DIGESTER - A horizontal digester built above ground on an east-west axis and painted black would heat up in the sun, more so if covered with plastic sheeting. If it gets too hot in the summer, remove the plastic and white wash the digester. Rather than bother with any measures outlined above, it is far simpler to be content with whatever amount of gas forms in the cold months and 'replace the shortage with some other fuel. One will then have cooked on free cowdung gas for nine months of the ye= l which is not at all bad. It is good to remember that cows' urine also ferments and forms gas. If a little of this is used with water for making the slurry, the output of gas is thereby increased. But too much urine is harmful: it would increase the ammonia content more than the bacteria can tolerate. About one-third of the water required can be replaced by urine. OUTPUT AND PRESSURE The output of gas varies with the pressure to which the fermenting slurry is subjected. Taking atmospheric pressure as normal (the drum being perfectlycounter- balanced), it has been found that under a pressure of 4" water head the production drops by 596, while under a negative pressure of 4!', production is about 10% above normal. In practice , however, a little gas may be sacrificed to convenience, the drum not being counterbalanced at all, but left floating on the slurry. There is thus a slight steady pressure at all times caused by the weight of the drum, and the gas is ready for use at any moment without one's having to go outside and remove balance weights. However, in colder climates where gas formation is less abundant, it may be wiser to counterbalance the drum and thus facilitate the production of gas. But it should be noted that a negative pressure could be dangerous if there is a slight leak in the gas drum on the delivery pipeline. Air is drawn in and the air-gas mixture may attain explosive proportions (596 - 15%).
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